1. Field of the Invention
The present invention relates to communication devices, and is more particularly concerned with an electro-optical modulator having a monomode light wave guide modulator.
2. Description of the Prior Art
The transmission of messages over light waveguides has a series of advantages. Included among such advantages are essentially: low signal attenuation; high bandwidth; and protection against disruption, particularly against electrical or magnetic fields. Added thereto are the high flexibility, the low weight, and the small dimensions of the light waveguides themselves, as well as the possibility offered by such waveguides of being able to realize potential separations in a simple manner.
Light waveguides are particularly employed in the higher levels of communication networks, particularly in telephone networks. They have already proven themselves in this application.
The transmission of messages, particularly speech, up to the subscriber over light waveguides is presently being tested. Broad-band services, for example, "cable television" and "telecopying", can be offered in the simplest manner with a corresponding transmission technique. The devices for these services are connected to the power supply network at the subscriber. This is not permissible for the operation of the telephone itself. Safety considerations of a technical and other nature play a decisive role here. One skilled in the art is familiar with the safety aspects of a technical nature. Other safety considerations lead to the requirement that a telephone installation remain operational in dangerous situations, even given outage of the power network.
The subscriber devices required for telephony must be supplied, therefore, with electrical energy which is available independently of the power supply network. According to an existing proposal, the subscriber devices are therefore supplied with energy from a exchange battery over copper lines laid in addition to the light waveguides, or they are supplied from batteries which are put in place at the subscriber device.
These additional copper lines or batteries can be eliminated when microphones are created which generate electrical signals in response to pressure and therefore make due without an electrical energy supply and are operational in conjunction with light waveguides. Considerable cost reductions would become possible by so doing.
Known solutions which have been proposed provide the employment of a device in which a light beam is reflected at a diaphragm subject to excursion due to acoustic pressure or pressure in general, being reflected in accordance with the excursion of the diaphragm, whereby a modulation of the input power is achieved, cf., for example, Frequenz 32 (1978), pp. 356-363, Fromm, I.: "Optofon-ein Optisches Ubertragungssystem fur Sprache". Given such devices, however, one must count on significant tolerance problems, particularly of the moving parts (diaphragm).